DIHYDRODIOL DEHYDROGENASE & PAH DETOXIFICATION

本申请要求支持研究事业

This application requests support for a Research Career Development Award for continuation of a systematic study of the role of dihydrodiol dehydrogenase in the detoxification of proximate and ultimate carcinogens of polycyclic aromatic hydrocarbons (PAH). The research programs includes chemical, biochemical, cellular and human studies designed to provide information on the role of this enzyme in PAH metabolism. We have shown that the homogeneous dihydrodiol dehydrogenase from rat liver cytosol oxidizes a variety of non-K-region-trans dihydrodiols of carcinogenic PAH to the corresponding ortho- quinones which can be trapped as mercaptoethanol adducts. To obtain information on this alternative pathway of proximate carcinogen metabolism, the reactivity of non-K-region ortho- quinone products towards cellular nucleophiles will be examined, the influence of bay-region methylation on reactivity will be determined, the ability of glutathione to enhance enzymatic rates of trans-dihydrodiol oxidation by trapping the ortho-quinone products will be assessed, structures of putative quinone- glutathione adducts will be elucidated, and the ability of these ortho-quinone products to act as substrates for highly purified preparations of rat liver glutathione transferases will be determined. The involvement of the homogeneous dihydrodiol dehydrogenase in ultimate carcinogen metabolism will be explored by using the stable anti-diol-epoxides of naphthalene and phenanthrene and the anti-diol epoxide of benzo(a)pyrene (BP) as substrates. Cellular studies will exploit the findings that the rat hepatoma cell line (H-4II-e) contains dihydrodiol dehydrogenase that is exquisitely sensitive to inhibition by indomethacin and 6- medroxyprogesterone acetate. By studying the metabolism of the (3H)-7,8-trans-dihydrodiol of BP in these cells, in the presence and absence of these drugs, the contribution of dihydrodiol dehydrogenase to the detoxification of PAH in whole cells will be assessed. If this enzyme plays a significant role these drugs should evaluate levels of anti-diol epoxides and BP-DNA adducts. To determine if dihydrodiol dehydrogenase plays a role in PAH metabolism in humans, liver autopsy samples will b analyzed for this enzyme activity, activities will be separated by chromatography and isozymes which oxidize the trans-7,8- dihydrodiol of BP will be characterized.